And Szczpcz to the contrary, you're not likely to learn anything useful in this situation. The OP is more likely to learn to muscle through the technique than anything else, and the uke isn't learning how his attack has left him open (if it is).
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If it is true, the sparring as a training tool in combat sports would be inefficient. However anybody knows that without sparring you can't learn how to fight efficiently...
So I believe the facts plays against your believes